Air conditioner and control method thereof

ABSTRACT

Disclosed herein are an air conditioner which controls a pressure of a refrigerant of an outdoor unit by adjusting an opening degree of an outdoor expansion valve or an indoor expansion valve, and a control method thereof. The air conditioner measures a pressure of the refrigerant discharged from a compressor during a cooling operation, and raises the pressure of the refrigerant to be higher than a designated pressure by controlling an opening degree of at least one of the outdoor expansion valve and the indoor expansion valve, if the pressure of the refrigerant is lower than the designated pressure. Further, the air conditioner measures the pressure of the refrigerant inhaled into the compressor during a heating operation, and adjusts the pressure of the refrigerant to be lower than a designated pressure by controlling the opening degree of the outdoor expansion valve, if the pressure of the refrigerant is higher than the designated pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority benefit of Korean PatentApplication No. 10-2010-0011651, filed on Feb. 8, 2010 in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference.

BACKGROUND

1. Field

Embodiments relate to an air conditioner to condition indoor air and acontrol method thereof.

2. Description of the Related Art

In general, air conditioners are cooling/heating apparatuses which coolor heat air of an indoor space, such as an office or a house, and form aseries of cycles consisting of compression, condensation, expansion, andevaporation. Such air conditioners discharge condensation heat orevaporation heat to an outdoor space mainly using air of the indoorspace.

Air conditioners are divided into an air cooling type air conditionerusing air as a heat source, a water cooling type air conditioner usingwater as a heat source, and a geothermal heat type air conditioner usingan underground heat source (a lake or a river), according to kinds ofheat sources.

Further, as is well known, air conditioners are divided into anintegrated type air conditioner in which an indoor unit conditioning airof an indoor space and an outdoor unit exchanging heat with arefrigerant circulated from the indoor unit are integrally formed, and asplit type air conditioner in which an indoor unit and an outdoor unitare separated from each other such that the indoor unit is installed inan indoor space and the outdoor unit is installed in an outdoor space.

SUMMARY

Therefore, it is an aspect to provide an air conditioner which controlsan opening degree of an electric expansion valve to maintain pressure ofa refrigerant of an outdoor unit in a high pressure range or a lowpressure range, and a control method thereof.

Additional aspects of the embodiments will be set forth in part in thedescription which follows and, in part, will be obvious from thedescription, or may be learned by practice of the embodiments.

In accordance with one aspect, a control method of an air conditioner,which has an outdoor unit including a compressor and an outdoorexpansion valve, and an indoor unit including an indoor expansion valve,includes measuring a pressure of a refrigerant discharged from thecompressor during a cooling operation, and raising the pressure of therefrigerant to be higher than a designated pressure by controlling anopening degree of at least one of the outdoor expansion valve and theindoor expansion valve, if the pressure of the refrigerant is lower thanthe designated pressure.

The opening degree of the indoor expansion valve may be controlled byadjusting a target superheat degree of the indoor unit, if the pressureof the refrigerant is lower than the designated pressure.

The opening degree of the indoor expansion valve may be decreased byraising the target superheat degree of the indoor unit, if the pressureof the refrigerant is lower than the designated pressure.

The pressure of the refrigerant may be raised to be higher than thedesignated pressure by decreasing the opening degree of the at least oneof the outdoor expansion valve and the indoor expansion valve, if thepressure of the refrigerant is lower than the designated pressure.

The outdoor unit may further include a receiver, and the pressure of therefrigerant transmitted to the indoor unit may be raised by transmittinghigh-pressure gas discharged from the compressor to the receiver, if thepressure of the refrigerant is lower than the designated pressure.

A superheat degree of the refrigerant transmitted to an inlet side ofthe compressor may be detected, and the superheat degree of therefrigerant transmitted to the inlet side of the compressor may beraised by decreasing the opening degree of the indoor expansion valve,if the superheat degree is lower than a designated reference.

In accordance with another aspect, a control method of an airconditioner, which has an outdoor unit including a compressor and anoutdoor expansion valve, and an indoor unit including an indoorexpansion valve, includes measuring a pressure of a refrigerant inhaledinto the compressor during a heating operation, and lowering thepressure of the refrigerant to be lower than a designated pressure bycontrolling an opening degree of the outdoor expansion valve, if thepressure of the refrigerant is higher than the designated pressure.

An amount of the refrigerant flowing in a direction of inhaling therefrigerant into the compressor may be decreased by decreasing theopening degree of the outdoor expansion valve, if the pressure of therefrigerant is higher than the designated pressure.

The opening degree of the outdoor expansion valve may be controlled byadjusting a superheat degree of the indoor unit.

In accordance with a further aspect, an air conditioner includes apressure sensor installed at a refrigerant outlet side of a compressorto measure a pressure of a refrigerant, and a control unit of an outdoorunit to raise the pressure of the refrigerant to be higher than adesignated pressure by controlling an opening degree of an outdoorexpansion valve, if the pressure of the refrigerant is lower than thedesignated pressure during a cooling operation.

The control unit of the outdoor unit may raise the pressure of therefrigerant to be higher than the designated pressure by decreasing theopening degree of the outdoor expansion valve, if the pressure of therefrigerant is lower than the designated pressure.

The air conditioner may further include a control unit of an indoor unitto raise the pressure of the refrigerant to be higher than a designatedpressure by controlling an opening degree of the indoor expansion valve,if the pressure of the refrigerant is lower than the designatedpressure.

The control unit of the indoor unit may raise the pressure of therefrigerant to be higher than the designated pressure by decreasing theopening degree of the indoor expansion valve, if the pressure of therefrigerant is lower than the designated pressure.

The control unit of the indoor unit may decrease the opening degree ofthe indoor expansion valve by adjusting a target superheat degree of theindoor unit.

The control unit of the indoor unit may decrease the opening degree ofthe indoor expansion valve by raising the target superheat degree of theindoor unit.

The air conditioner may further include a pressure sensor installed at arefrigerant inlet side of the compressor to measure the pressure of therefrigerant, and a control unit of an indoor unit to receive dataregarding the pressure of the refrigerant from the pressure sensor,installed at the refrigerant inlet side of the compressor, during aheating operation, and to adjust the pressure of the refrigerant to belower than a designated pressure by controlling a target superheatdegree of the refrigerant inhaled into the compressor, if the pressureof the refrigerant is higher than the designated pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects of the embodiments will become apparent andmore readily appreciated from the following description of theembodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a schematic view illustrating an installation state of a watercooling type air conditioner in accordance with one embodiment;

FIG. 2 is a block diagram illustrating a configuration of the airconditioner in accordance with the embodiment;

FIG. 3 is a control block diagram of the air conditioner in accordancewith the embodiment;

FIG. 4 is a flow chart illustrating a method of maintaining highpressure of a refrigerant by controlling an opening degree of an outdoorexpansion valve during a cooling operation of an air conditioner inaccordance with one embodiment;

FIG. 5 is a flow chart illustrating a method of maintaining low pressureof a refrigerant by controlling an opening degree of an outdoorexpansion valve during a heating operation of an air conditioner inaccordance with another embodiment;

FIG. 6 is a flow chart illustrating a method of maintaining highpressure of a refrigerant by controlling an opening degree of an indoorexpansion valve during a cooling operation of an air conditioner inaccordance with another embodiment; and

FIG. 7 is a flow chart illustrating a method of adjusting a superheatdegree of an inhaled refrigerant of a compressor by controlling asuperheat degree of an indoor unit during a cooling operation of an airconditioner in accordance with another embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to like elements throughout.

FIG. 1 is a schematic view illustrating an installation state of a watercooling type air conditioner in accordance with one embodiment, and FIG.2 is a block diagram illustrating a configuration of the air conditionerin accordance with the embodiment.

With reference to FIGS. 1 and 2, the water cooling type air conditioneris installed to condition air of indoor spaces within a large-scalebuilding or a high-rise building provided with the plural indoor spaces.Therefore, a building in which the water cooling type air conditioner isinstalled is provided with plural indoor spaces, and the water coolingtype air conditioner serves to condition air of the plural indoorspaces.

In the air conditioner in accordance with this embodiment, indoor units100 are respectively installed in plural indoor spaces provided in abuilding, and an air conditioning room A, in which an outdoor unit 200connected with the plural indoor spaces 100 by pipes is installed, isprovided at the side of the indoor spaces in which the indoor units 100are respectively installed.

In each indoor space, the indoor unit 100 in a type suited to eachindoor space is installed, thus conditioning air in each indoor space.That is, indoor units 100 of various models, i.e., a stand type, aceiling-mounted type, and a wall-mounted type, may be used according touser selection. These indoor units 100 are connected with the outdoorunit 200 by refrigerant pipes 300, and the refrigerant pipes 300 guideflow of a refrigerant between the indoor units 100 and the outdoor unit200.

The refrigerant pipes 300 are installed so as to connect the indoorunits 100 and the outdoor unit 200, and are formed in the shape of acircular pipe having a designated diameter such that the refrigerantserving as an operating fluid flows along the inner spaces of therefrigerant pipes 300. Therefore, the refrigerant pipes 300 are branchedoff from the refrigerant pipe 300 connected to the outdoor unit 200, andare connected to the respective indoor units 100.

A cooling tower 400 to cool water to generate cooling water is installedon the top of the building in which the water cooling type airconditioner is installed. The cooling tower 400 causes water to directlycontact air, thereby cooling water to generate cooling water.

The cooling water generated in the inner space of the cooling tower 400is guided to the inner space of the outdoor unit 200 by a cooling watersupply pipe 420. The cooling water exchanges heat with the refrigerantin the outdoor unit 200, is guided to the upper end of the cooling tower400 by a cooling water recovery pipe 440, is again cooled in the coolingtower 400, and then flows to the inner space of the outdoor unit 200.This process is repeated.

A cooling water pump 460 is mounted on the cooling water supply pipe420, and supplies the cooling water generated from the cooling tower 400to the inner space of the outdoor unit 200 at a regular pressure.

An indoor heat exchanger 120 to inhale or pull air in the indoor spaceand to perform heat exchange of the inhaled air with the refrigerant tocondition the air in the indoor space is mounted in the indoor unit 100.The indoor heat exchanger 120 is formed by bending a circular pipehaving a designated diameter several times, and the refrigerant servingas the operating fluid flows within the indoor heat exchanger 120.

An indoor expansion valve 140 to adjust an amount of the refrigerantintroduced into the indoor heat exchanger 120 or the refrigerantdischarged from the indoor heat exchanger 120 is provided in the indoorunit 100. The indoor expansion valve 140 expands the refrigerant passingtherethrough, thereby reducing the pressure of the refrigerant.

The refrigerant pipes 300 are connected between the indoor units 100 andthe outdoor unit 200 such that the refrigerant is circulated through therefrigerant pipes 300. The refrigerant pipes 300 include high pressurepipes through which the refrigerant of a high pressure flows, and lowpressure pipes through which the refrigerant of a low pressure flows.The refrigerant pipes 300 are branched off from the refrigerant pipe 300connected to the outdoor unit 200, and are connected to the respectiveindoor units 100, thereby guiding the refrigerant to the insides of theindoor heat exchangers 120.

Therefore, the refrigerant flowing along the refrigerant pipe 300 isintroduced into the outdoor unit 200 and exchanges heat with the coolingwater guided by the cooling water supply pipe 420, and the refrigeranthaving exchanged heat moves to the insides of the indoor heat exchangers120 along the refrigerant pipes 300, exchanges heat with air of theindoor spaces, in which the indoor units 100 are respectively installed,and thus conditions the air in the indoor spaces.

Further, the cooling water having exchanged heat with the refrigerantwithin the outdoor unit 200 flows to the inner space of the coolingtower 400 along the cooling water recovery pipe 440, thus forming onecycle.

With reference to FIG. 2, an inner configuration of the outdoor unit 200will be described in more detail. An oil separator 265 and a refrigeranthigh pressure sensor 241 are provided at an output side of a compressor260. The oil separator 265 separates oil contained in the refrigerant,which is compressed into a high temperature and high pressure state inthe compressor 260 and is discharged to the outside of the compressor260 together with the refrigerant, from the refrigerant. The refrigeranthigh pressure sensor 241 is installed in a high pressure pipe andmeasures high pressure of the refrigerant discharged from the compressor260.

The oil separator 265 is formed in the shape of a cylinder havingdesignated diameter and height. The oil separator 265 causes the oil toflow into the compressor 260 so as to cool frictional heat generated dueto driving of the compressor 260, and the oil having flown into thecompressor 260, is contained in the refrigerant compressed into the hightemperature and high pressure state in the compressor 260 and isdischarged to the outside of the compressor 260. The oil contained inthe refrigerant and discharged to the outside of the compressor 260 isseparated from the refrigerant by the oil separator 265, and is returnedto the compressor 260 via an oil recovery pipe 271.

The oil separator 265 is connected to a refrigerant control valve 270 bya pipe. The refrigerant control valve 270 employs a four-way valve, andserves to convert a flow direction of the refrigerant according tooperation modes of the water cooling type air conditioner. Among portsof the refrigerant control valve 270, one port is connected to the oilseparator 265, and the remaining ports are connected to the indoor heatexchangers 120, an outdoor heat exchanger 230, and an accumulator 264 bypipes.

One end of the pipe connecting one port among the ports of therefrigerant control valve 280 to the outdoor heat exchanger 230 isconnected to a refrigerant inlet side 233 through which the refrigerantis introduced to the inner space of the outdoor heat exchanger 230, anda refrigerant outlet side 234 through which the refrigerant having beenintroduced into the outdoor heat exchanger 230 through the refrigerantinlet side 233 and exchanged heat with cooling water in the outdoor heatexchanger 230 is discharged from the outdoor heat exchanger 230 isconnected to the indoor heat exchangers 120 by an pipe.

An outdoor expansion valve 280 is mounted on the pipe connecting therefrigerant output 234 and the indoor heat exchangers 120.

A supercooler 282 to supercool the refrigerant is provided between theoutdoor expansion valve 280 and the indoor heat exchangers 120. Thesupercooler 282 is a device to supercool the refrigerant havingexchanged heat in the indoor heat exchangers 120 and the outdoor heatexchanger 230.

The accumulator 264 to temporarily store the refrigerant is provided onthe pipe between the indoor heat exchangers 120 and the compressor 260.The accumulator 264 separates a refrigerant in a gaseous state from therefrigerant introduced into the compressor 260 such that only therefrigerant in the gaseous state flows into the compressor 260. Theaccumulator 264 temporarily stores the refrigerant introduced to aninlet side of the compressor 260 from the outdoor heat exchanger 230 orthe indoor heat exchangers 120. The accumulator 264 divides theintroduced refrigerant into the refrigerant in the gaseous state and arefrigerant in a liquid state. The refrigerant in the gaseous stateseparated by the accumulator 264 is inhaled to the low pressure inletside of the compressor 260.

A refrigerant low pressure sensor 242 and a temperature sensor 243 areprovided between the accumulator 264 and the compressor 260. Therefrigerant low pressure sensor 242 measures a low pressure of therefrigerant introduced into the inlet side of the compressor 260, andthe temperature sensor 243 measures a temperature of the refrigerantintroduced into the inlet side of the compressor 260.

Although FIGS. 1 and 2 illustrate the water cooling type air conditionerusing water as a heat exchange source with the refrigerant flowing inthe outdoor heat exchanger 230, the embodiments may be applied to ageothermal heat type air conditioner using geothermal heat as a heatexchange source. The geothermal heat type air conditioner is buriedunderground or under surface water, such as a lake or a river, so as toexchange heat with heat source water, and has the same configuration asthat of the water cooling type air conditioner except that thegeothermal heat type air conditioner uses geothermal heat as the heatexchange.

FIG. 3 is a control block diagram of the air conditioner in accordancewith the embodiment.

The outdoor unit 200 and the indoor unit 100 include sensor units 101and 201, control units 102 and 202, storage units 103 and 203,communication units 105 and 205, and driving units 104 and 204,respectively.

The sensor unit 201 of the outdoor unit 200 includes the refrigeranthigh pressure sensor 241, the refrigerant low pressure sensor 242, andthe temperature sensor 243. The refrigerant high pressure sensor 241 isinstalled at the outlet side of the compressor 260, and measures a highpressure of the refrigerant discharged from the compressor 260. Therefrigerant low pressure sensor 242 is installed at the inlet side ofthe compressor 260, and measures a low pressure of the refrigerantinhaled into the compressor 260. The temperature sensor 243 is installedat the inlet side of the compressor 260, and measures a temperature ofthe refrigerant.

The control unit 202 of the outdoor unit 200 controls the pressure ofthe refrigerant of the outdoor unit 200 in a designated high pressurerange during a cooling operation. The control unit 202 of the outdoorunit 200 controls an opening degree of the outdoor expansion valve 280according to data regarding the high pressure of the refrigeranttransmitted from the refrigerant high pressure sensor 241 during thecooling operation, thus maintaining the high pressure of the refrigerantat a designated level. The control unit 202 of the outdoor unit 200detects the high pressure of the refrigerant discharged from thecompressor 260 through the refrigerant high pressure sensor 241, anddecreases the opening degree of the outdoor expansion valve 280, if thehigh pressure of the refrigerant is lower than a reference pressure,thus raising the high pressure of the refrigerant. If the opening degreeof the outdoor expansion valve 280 is decreased, an amount of therefrigerant discharged from the outdoor heat exchanger 230 to a receiver290 is decreased, and thus an amount of the refrigerant between thecompressor 260 and the outdoor heat exchanger 230 is increased and thepressure of the refrigerant at the outlet side of the compressor 260 israised.

The control unit 202 of the outdoor unit 200 detects the high pressureof the refrigerant discharged from the compressor 260 through therefrigerant high pressure sensor 241, and transmits a high pressure gasof the compressor 260 to the receiver 290, if the high pressure of therefrigerant is lower than the reference pressure. When the high pressuregas is supplied to the receiver 290, the pressure of the refrigerant isoutput from the receiver 290 to the indoor units 100 is raised, thuspreventing lowering of the performance of the indoor units 100.

The control unit 202 of the outdoor unit 200 controls the pressure ofthe refrigerant of the outdoor unit 200 in a designated low pressurerange during a heating operation. The control unit 202 of the outdoorunit 200 controls the opening degree of the outdoor expansion valve 280according to data regarding the low pressure of the refrigeranttransmitted from the refrigerant low pressure sensor 242 during theheating operation, thus maintaining the low pressure of the refrigerantat a designated level. The control unit 202 of the outdoor unit 200detects the low pressure of the refrigerant discharged from thecompressor 260 using the refrigerant low pressure sensor 242, anddecreases the opening degree of the outdoor expansion valve 280, if thelow pressure of the refrigerant is higher than a reference pressure, andthus lowers the low pressure of the refrigerant. If the opening degreeof the outdoor expansion valve 280 is decreased, an amount of therefrigerant flowing from the receiver 290 to the outdoor heat exchanger230 is decreased, and thus an amount of the refrigerant flowing throughthe indoor heat exchangers 230 to the accumulator 264 is decreased andthe pressure of the refrigerant at the inlet side of the compressor 260is lowered.

The control unit 202 of the outdoor unit 200 adjusts a superheat degreeof the inhaled refrigerant of the compressor 260 according to the dataregarding the low pressure of the refrigerant transmitted from therefrigerant low pressure sensor 242 during the heating operation, thuscontrolling the opening degree of the outdoor expansion valve 280. Thesuperheat degree of the inhaled refrigerant of the compressor 260 isobtained by Expression 1 below.

Superheat Degree of Inhaled Refrigerant=Temperature of InhaledRefrigerant−Saturation Temperature of Inhaled Refrigerant  Expression 1

In Expression 1, the temperature of the inhaled refrigerant is measuredby the temperature sensor 243 installed at the inlet side of thecompressor 260, and the saturation temperature of the inhaledrefrigerant is determined by the pressure of the refrigerant measured bythe refrigerant low pressure sensor 242 installed at the inlet side ofthe compressor 260. Saturation temperatures according to pressures ofthe refrigerant are stored in advance in the storage unit 203. Forexample, when the pressure of the refrigerant measured by therefrigerant low pressure sensor 242 is 7 kg/cm², the saturationtemperature corresponding to this pressure which is stored in advance inthe storage unit 203 is about 0° C. Hereinafter, a method of controllingthe opening degree of the outdoor expansion valve 280 by adjusting thesuperheat degree of the inhaled refrigerant will be described.

The control unit 202 of the outdoor unit 200 detects the low pressure ofthe refrigerant inhaled into the compressor 260 using the refrigerantlow pressure sensor 242, and increases the superheat degree of theinhaled refrigerant, if the low pressure of the refrigerant is higherthan the reference pressure. In order to increase the superheat degreeof the inhaled refrigerant of the compressor 260, the opening degree ofthe outdoor expansion valve 280 is decreased. If the opening degree ofthe outdoor expansion valve 280 is decreased, the amount of therefrigerant flowing from the receiver 290 to the outdoor heat exchanger230 is decreased, the refrigerant greatly exchanges heat in the outdoorheat exchanger 230 and thus the temperature of the refrigerant israised, and the refrigerant having the raised temperature flows to thecompressor 260 via the accumulator 264. During this process, thetemperature of the inhaled refrigerant of the compressor 260 is raised,and thus the superheat degree of the inhaled refrigerant of thecompressor 260 is increased with reference to Expression 1. Further, ifthe opening degree of the outdoor expansion valve 280 is decreased, thepressure of the inhaled refrigerant of the compressor 260 is loweredthrough the above-described process, and thus the pressure of therefrigerant measured by the refrigerant low pressure sensor 242installed at the inlet side of the compressor 260 may be lowered.

The storage unit 203 of the outdoor unit 200 stores saturationtemperatures according to pressures of the refrigerant.

The communication unit 205 of the outdoor unit 200 receives datatransmitted from the indoor units 100, or transmits data to the indoorunits 100.

The driving unit 204 of the outdoor unit 200 drives the compressor 260and the outdoor expansion valve 280 under the control of the controlunit 202.

The sensor unit 101 of the indoor unit 100 includes temperature sensors161 and 162. The temperature sensors 161 and 162 of the sensor unit 101are installed at inlet side and outlets of the indoor heat exchanger120, and measure the temperature of the refrigerant.

The control unit 102 of the indoor unit 100 controls an opening degreeof the indoor expansion valve 140 according to data regarding the highpressure of the refrigerant transmitted from the communication unit 205of the outdoor unit 200 during the cooling operation, thus maintainingthe high pressure of the refrigerant of the outdoor unit 200 at adesignated level. The communication unit 105 of the indoor unit 100receives data transmitted from the outdoor unit 200 through thecommunication unit 205, and the control unit 102 of the indoor unit 100controls the opening degree of the indoor expansion valve 140 accordingto the data transmitted from the outdoor unit 200. If the opening degreeof the indoor expansion valve 140 is decreased, an amount of therefrigerant input to the indoor unit 100 is decreased, and if the amountof the refrigerant input to the indoor unit 100 is decreased, an amountof the refrigerant staying in the outdoor unit 200 is increased and thusthe pressure of the refrigerant of the outdoor unit 200 is raised.

The control unit 102 of the indoor unit 100 adjusts a superheat degreeof the indoor unit 100 according to the superheat degree of the inhaledrefrigerant of the compressor 260, transmitted from the communicationunit 205 of the outdoor unit 200, thus maintaining the pressure of therefrigerant of the outdoor unit 200 at a designated high pressure. Thesuperheat degree of the inhaled refrigerant of the compressor 260 isobtained by Expression 1, which is described above, and the superheatdegree of the indoor unit 100 is obtained by Expression 2, below.

Superheat Degree of Indoor Unit=Temperature of Outlet of Indoor HeatExchanger−Temperature of Inlet of Indoor Heat Exchanger  Expression 2

In Expression 2, the outlet of the indoor heat exchanger 120 means aside surface of the indoor heat exchanger 120 through which therefrigerant is discharged to the outside of the indoor heat exchanger120 during the cooling operation, and the inlet of the indoor heatexchanger 120 means a side surface of the indoor heat exchanger throughwhich the refrigerant is introduced into the indoor heat exchanger 120during the cooling operation. Hereinafter, a method of adjusting thepressure of the refrigerant of the outdoor unit 200 to a designated highpressure by adjusting the superheat degree of the indoor unit 100according to the superheat degree of inhaled refrigerant of thecompressor 260 will be described in detail.

If the superheat degree of the inhaled refrigerant of the compressor 260during the cooling operation is lowered, the control unit 202 of theoutdoor unit 200 transmits designated data to the control unit 102 ofthe indoor unit 100, thus increasing the superheat degree of the indoorunit 100. In order to increase the superheat degree of the indoor unit100, the opening degree of the indoor expansion valve 140 needs to bedecreased. If the opening degree of the indoor expansion valve 140 isdecreased, the amount of the refrigerant introduced into the indoor heatexchanger 120 is decreased, and if the amount of the refrigerantintroduced into the indoor heat exchanger 120 is decreased, therefrigerant greatly exchanges heat in the indoor heat exchanger 120 andthus is discharged through the outlet of the indoor heat exchanger 120under the condition that the temperature of the refrigerant is moreincreased than that of the refrigerant if the amount of the refrigerantis increased. (During the cooling operation, the temperature of theoutlet side of the indoor heat exchanger is higher than the temperatureof the inlet side of the indoor heat exchanger). With reference toExpression 2, it is understood that the temperature of the outlet of theindoor heat exchanger 120 is more raised and thus the superheat degreeof the indoor unit 100 is increased. Further, since the temperature ofthe refrigerant transmitted from the indoor unit 100 to the outdoor unit200 is raised, the temperature of the refrigerant flowing to the inletside of the compressor 260 is raised, and thereby the superheat degreeof the inhaled refrigerant of Expression 1 is increased.

On the other hand, with reference to Expression 1, it is understood thatthe reason why the superheat degree of the inhaled refrigerant islowered is that the temperature of the inhaled refrigerant is lowered orthe saturation temperature of the inhaled refrigerant is raised.Hereinafter, the saturation temperature of the inhaled refrigerant has amuch smaller variation than that of the temperature of the inhaledrefrigerant, and thus a case that the temperature of the inhaledrefrigerant is lowered will be exemplarily described.

The temperature of the inhaled refrigerant is lowered, if the amount ofthe refrigerant transmitted from the indoor heat exchanger 120 to theoutdoor unit 200 is large (the large amount of the refrigerant causingpoor evaporation), or if the refrigerant having poorly exchanged heatdue to load abnormality of the indoor heat exchanger 120 is transmittedto the outdoor unit 200. In case of the former, the refrigerant of theoutdoor unit 200 may be in a high pressure state already (or may be in alow pressure state), and in case of the latter, the pressure of therefrigerant of the outdoor unit 200 may be in a high pressure state or alow pressure state. Thereby, the control unit 102 of the indoor unit 100may adjust the superheat degree of the indoor unit 100 to a high level,if the pressure of the refrigerant of the outdoor unit 200 is low andthe superheat degree of the inhaled refrigerant of the compressor 260 islow. If the superheat degree of the indoor unit 100 is adjusted to thehigh level, as described above, the opening degree of the indoorexpansion valve 140 is decreased, and if the opening degree of theindoor expansion valve 140 is decreased, an amount of the refrigerantstaying in the outdoor unit 200 is increased and thus the pressure ofthe refrigerant of the outdoor unit 200 is raised. On the other hand, ifthe pressure of the refrigerant of the outdoor unit 200 is high, thesuperheat degree of the inhaled refrigerant of the compressor 260 may beincreased by increasing the superheat degree of the indoor unit 100.Here, the pressure of the refrigerant of the outdoor unit 200 may befurther raised by decreasing the opening degree of the indoor expansionvalve 140, but is generally adjusted by a separate control method.

The communication unit 105 of the indoor unit 100 receives datatransmitted from the outdoor unit 200, or transmits data to thecommunication unit 205 of the outdoor unit 200.

The storage unit 103 of the indoor unit 100 stores various data used tooperate the indoor unit 100. The storage unit 103 of the indoor unit 100stores the superheat degree to be adjusted according to the superheatdegree of the inhaled refrigerant of the compressor 260. The drivingunit 104 of the indoor unit 100 drives the indoor expansion valve 140and so on.

FIG. 4 is a flow chart illustrating a method of maintaining highpressure of a refrigerant by controlling an opening degree of an outdoorexpansion valve during the cooling operation of an air conditioner inaccordance with one embodiment.

When the cooling operation is started, the control unit 202 of theoutdoor unit 200 adjusts the opening degree of the outdoor expansionvalve 280 to S₁ (operation 500).

Thereafter, the control unit 202 of the outdoor unit 200 receives dataregarding the high pressure of the refrigerant transmitted from therefrigerant high pressure sensor 241 installed at the refrigerant outletside of the compressor 260 (operation 501).

Thereafter, the control unit 202 of the outdoor unit 200 compares thehigh pressure P_(h) of the refrigerant measured during operation 501with a first reference pressure P₁ (operation 502), and adjusts theopening degree of the outdoor expansion valve 280 to S₂, if the highpressure P_(h) of the refrigerant is lower than the first referencepressure P₁ (operation 503). That is, the control unit 202 of theoutdoor unit 200 decreases the opening degree of the outdoor expansionvalve 280, thereby raising the pressure of the refrigerant of theoutdoor unit 200.

On the other hand, the control unit 202 of the outdoor unit 200 comparesthe high pressure P_(h) of the refrigerant with a second referencepressure P₂, if the high pressure P_(h) of the refrigerant is higherthan the first reference pressure P₁ (operation 504), and adjusts theopening degree of the outdoor expansion valve 280 to S₃, if the highpressure P_(h) of the refrigerant is higher than the second referencepressure P₂ (operation 505). That is, the control unit 202 of theoutdoor unit 200 increases the opening degree of the outdoor expansionvalve 280, thereby lowering the pressure of the refrigerant of theoutdoor unit 200.

Further, the control unit 202 of the outdoor unit 200 maintains theopening degree of the outdoor expansion valve 280 to S₁, if the highpressure P_(h) of the refrigerant is lower than the second referencepressure P₂ (operation 506), and then the process is fed back tooperation 500.

Here, S₁, S₂, and S₃ represent opening degrees of the outdoor expansionvalve 280, and for example, satisfy an equation of S₂<S₁<S₃. Further,the control unit 202 of the outdoor unit 200 judges that air conditionerreaches a normal state, when an equation of P₁<P_(h)<P₂ is satisfied.

FIG. 5 is a flow chart illustrating a method of maintaining low pressureof a refrigerant by controlling an opening degree of an outdoorexpansion valve during a heating operation of an air conditioner inaccordance with another embodiment.

When the heating operation is started, the control unit 202 of theoutdoor unit 200 adjusts the opening degree of the outdoor expansionvalve 280 to SH₁. The adjustment of the opening degree of the outdoorexpansion valve 280 to SH₁ means adjustment of the opening of theoutdoor expansion valve 280 according to the superheat degree of theinhaled refrigerant of the compressor 260. That is, the control unit 202of the outdoor unit 200 adjusts the opening degree of the outdoorexpansion valve 280 according to the superheat degree of the inhaledrefrigerant of the compressor 260 (operation 510).

Thereafter, the control unit 202 of the outdoor unit 200 receives dataregarding the low pressure of the refrigerant transmitted from therefrigerant low pressure sensor 242 installed at the refrigerant inletside of the compressor 260. The refrigerant low pressure sensor 242 is apressure sensor mounted at the inlet side of the compressor 260(operation 511).

Thereafter, the control unit 202 of the outdoor unit 200 compares thelow pressure P_(L) of the refrigerant measured during operation 511 witha third reference pressure P₃ (operation 512), and maintains or adjuststhe opening degree of the outdoor expansion valve 280 to SH₁, if the lowpressure P_(L) of the refrigerant is lower than the third referencepressure P₃ (operation 514).

On the other hand, the control unit 202 of the outdoor unit 200 comparesthe low pressure P_(L) of the refrigerant measured during operation 511with a fourth reference pressure P₄, if the low pressure P_(L) of therefrigerant is higher than the third reference pressure P₃ (operation513), and adjusts the opening degree of the outdoor expansion valve 280to SH₂ (for example, adjusts the opening degree of the outdoor expansionvalve 280 according to superheat of 10° C.), if the low pressure P_(L)of the refrigerant is lower than the fourth reference pressure P₄(operation 515). That is, the control unit 202 of the outdoor unit 200decreases the opening degree of the outdoor expansion valve 280, therebylowering the pressure of the refrigerant of the outdoor unit 200.

Further, the control unit 202 of the outdoor unit 200 adjusts theopening degree of the outdoor expansion valve 280 to SH₃ (for example,adjusts the opening degree of the outdoor expansion valve 280 accordingto superheat of 15° C.), if the low pressure P_(L) of the refrigerantmeasured during operation 511 is lower than the fourth referencepressure P₄ (operation 513 and operation 516).

Here, SH₁, SH₂, and SH₃ mean target superheat degrees to adjust theopening degree of the outdoor expansion valve 280, and for example,satisfy an equation of SH₁<SH₂<SH₃.

FIG. 6 is a flow chart illustrating a method of maintaining highpressure of a refrigerant by controlling an opening degree of an indoorexpansion valve during a cooling operation of an air conditioner inaccordance with another embodiment.

When the cooling operation is started, the control unit 102 of theindoor unit 100 adjusts the opening degree of the indoor expansion valve140 to ID_SH₁. ID_SH₁ (Indoor_Super Heat1) means a target superheat tocontrol the opening degree of the indoor expansion valve 140. Forexample, the adjustment of the opening degree of the indoor expansionvalve 140 to ID_SH₁ is achieved by adjusting the opening degree of theindoor expansion valve 140 to control superheat of 2° C. of the indoorunit 100 (operation 520).

Thereafter, the control unit 102 of the indoor unit 100 receives dataregarding the high pressure of the refrigerant at the outlet side of thecompressor 260, transmitted from the communication unit 205 of theoutdoor unit 200 (operation 521).

Thereafter, the control unit 102 of the indoor unit 100 compares thehigh pressure P_(h) of the refrigerant with a fifth reference pressureP₅ (operation 522), and adjusts the opening degree of the indoorexpansion valve 140 to ID_SH₂, if the high pressure P_(h) of therefrigerant is lower than the fifth reference pressure P₅ (operation523). That is, the control unit 102 of the indoor unit 100 decreases theopening degree of the indoor expansion valve 140, thereby raising thepressure of the refrigerant of the outdoor unit 200.

On the other hand, the control unit 102 of the indoor unit 100 maintainsor adjusts the opening degree of the indoor expansion valve 140 toID_SH₁, if the high pressure P_(h) of the refrigerant transmitted fromoperation 521 is higher than the fifth reference pressure P₅, and theprocess is fed back to operation 521 (operation 522 and operation 524).

Here, ID_SH₁ and ID_SH₂ mean target superheat degrees to control theopening degree of the indoor expansion valve 140, and for example,satisfy an equation of ID_SH₁<ID_SH₂.

FIG. 7 is a flow chart illustrating a method of adjusting a superheatdegree of an inhaled refrigerant of a compressor by controlling asuperheat degree of an indoor unit during a cooling operation of an airconditioner in accordance with another embodiment.

When the cooling operation is started, the control unit 102 of theindoor unit 100 adjusts the opening degree of the indoor expansion valve140 to ID_SH₃. ID_SH₃ (Indoor_Super Heat3) represents the opening degreeof the indoor expansion valve 140 according to the superheat degree ofthe indoor unit 100. For example, ID_SH₃ represents the opening degreeof the indoor expansion valve 140 according to superheat of 4° C. of theindoor unit 100 (operation 530).

Thereafter, the communication unit 105 of the indoor unit 100 receivesdata regarding the superheat degree of the inhaled refrigerant of thecompressor 260, transmitted from the communication unit 205 of theoutdoor unit 200 (operation 531).

Therefore, the control unit 102 of the indoor unit 100 compares thesuperheat degree of the inhaled refrigerant of the compressor 260 with afirst reference value (operation 532), and maintains or adjusts theopening degree of the indoor expansion valve 140 to ID_SH₃, if thesuperheat degree of the inhaled refrigerant is lower than the firstreference pressure value (operation 534). When the superheat degree ofthe inhaled refrigerant of the compressor 260 is low, the opening degreeof the indoor expansion valve 140 is maintained or adjusted to a lowvalue and thus an amount of the refrigerant transmitted to the outdoorunit 200 is decreased. When the amount of the refrigerant transmitted tothe outdoor unit 200 is decreased, the refrigerant greatly exchangesheat in the indoor heat exchanger 120, as described above, and when therefrigerant greatly exchanges heat in the indoor heat exchanger 120, thetemperature of the refrigerant transmitted to the inlet side of thecompressor 260 is raised, and thus the superheat degree of the inhaledrefrigerant of the compressor 260 is raised

On the other hand, the control unit 102 of the indoor unit 100 comparesthe superheat degree of the inhaled refrigerant of the compressor 260with a second reference value, if the superheat degree of the inhaledrefrigerant of the compressor 260 is higher than the second referencepressure value (operation 533). The control unit 102 of the indoor unit100 maintains or adjusts the opening degree of the indoor expansionvalve 140 to ID_SH₄, if the superheat degree of the inhaled refrigerantof the compressor 260 is lower than the second reference pressure value(operation 535). ID_SH₄ represents a state in which the opening degreeof the indoor expansion valve 140 according to the control of thesuperheat degree is lower than that of than ID_SH₃.

Further, the control unit 102 of the indoor unit 100 maintains oradjusts the opening degree of the indoor expansion valve 140 to ID_SH₅,if the superheat degree of the inhaled refrigerant of the compressor 260is higher than the second reference pressure value (operation 536).ID_SH₅ represents a state in which the opening degree of the indoorexpansion valve 140 according to the control of the superheat degree islower than that of ID_SH₄.

The embodiment of FIG. 7, which illustrates control of the superheatdegree of the refrigerant inhaled into the compressor 260 by adjustingthe superheat degree of the indoor unit 100, may be carried out togetherwith the embodiments of FIGS. 4 to 6.

Although the above embodiments separately illustrate control of theopening degree of the indoor expansion valve 140 and control of theopening degree of the outdoor expansion valve 280, control of theopening degree of the indoor expansion valve 140 and control of theopening degree of the outdoor expansion valve 280 may be simultaneouslyperformed by the control unit 202 of the outdoor unit 200 and thecontrol unit 102 of the indoor unit 100.

As is apparent from the above description, in an air conditioner and acontrol method thereof in accordance with one embodiment, the pressureof a refrigerant of an outdoor unit is maintained at a regular levelduring a heating operation or a cooling operation, thereby obtainingreliability in operation of the air conditioner.

Although a few embodiments have been shown and described, it would beappreciated by those skilled in the art that changes may be made inthese embodiments without departing from the principles and spirit ofthe embodiments, the scope of which is defined in the claims and theirequivalents.

1. A control method of an air conditioner, which has an outdoor unitincluding a compressor and an outdoor expansion valve, and an indoorunit including an indoor expansion valve, comprising: measuring apressure of a refrigerant discharged from the compressor during acooling operation; and raising the pressure of the refrigerant to behigher than a designated pressure by controlling an opening degree of atleast one of the outdoor expansion valve and the indoor expansion valve,if the pressure of the refrigerant is lower than the designatedpressure.
 2. The control method according to claim 1, wherein theopening degree of the indoor expansion valve is controlled by adjustinga target superheat degree of the indoor unit, if the pressure of therefrigerant is lower than the designated pressure.
 3. The control methodaccording to claim 2, wherein the opening degree of the indoor expansionvalve is decreased by raising the target superheat degree of the indoorunit, if the pressure of the refrigerant is lower than the designatedpressure.
 4. The control method according to claim 1, wherein thepressure of the refrigerant is raised to be higher than the designatedpressure by decreasing the opening degree of the at least one of theoutdoor expansion valve and the indoor expansion valve, if the pressureof the refrigerant is lower than the designated pressure.
 5. The controlmethod according to claim 1, wherein: the outdoor unit further includesa receiver; and the pressure of the refrigerant transmitted to theindoor unit is raised by transmitting high-pressure gas discharged fromthe compressor to the receiver, if the pressure of the refrigerant islower than the designated pressure.
 6. The control method according toclaim 1, wherein: a superheat degree of the refrigerant transmitted toan inlet side of the compressor is detected; and the superheat degree ofthe refrigerant transmitted to the inlet side of the compressor israised by decreasing the opening degree of the indoor expansion valve,if the superheat degree is lower than a designated reference.
 7. Acontrol method of an air conditioner, which has an outdoor unitincluding a compressor and an outdoor expansion valve, and an indoorunit including an indoor expansion valve, comprising: measuring apressure of a refrigerant inhaled into the compressor during a heatingoperation; and lowering the pressure of the refrigerant to be lower thana designated pressure by controlling an opening degree of the outdoorexpansion valve, if the pressure of the refrigerant is higher than thedesignated pressure.
 8. The control method according to claim 7, whereinan amount of the refrigerant flowing in a direction of inhaling therefrigerant into the compressor is decreased by decreasing the openingdegree of the outdoor expansion valve, if the pressure of therefrigerant is higher than the designated pressure.
 9. The controlmethod according to claim 7, wherein the opening degree of the outdoorexpansion valve is controlled by adjusting a superheat degree of theindoor unit.
 10. An air conditioner comprising: a pressure sensorinstalled at a refrigerant outlet side of a compressor to measure apressure of a refrigerant; and a control unit of an outdoor unit toraise the pressure of the refrigerant to be higher than a designatedpressure by controlling an opening degree of an outdoor expansion valve,if the pressure of the refrigerant is lower than the designated pressureduring a cooling operation.
 11. The air conditioner according to claim10, wherein the control unit of the outdoor unit raises the pressure ofthe refrigerant to be higher than the designated pressure by decreasingthe opening degree of the outdoor expansion valve, if the pressure ofthe refrigerant is lower than the designated pressure.
 12. The airconditioner according to claim 10, further comprising a control unit ofan indoor unit to raise the pressure of the refrigerant to be higherthan a designated pressure by controlling an opening degree of theindoor expansion valve, if the pressure of the refrigerant is lower thanthe designated pressure.
 13. The air conditioner according to claim 12,wherein the control unit of the indoor unit raises the pressure of therefrigerant to be higher than the designated pressure by decreasing theopening degree of the indoor expansion valve, if the pressure of therefrigerant is lower than the designated pressure.
 14. The airconditioner according to claim 13, wherein the control unit of theindoor unit decreases the opening degree of the indoor expansion valveby adjusting a target superheat degree of the indoor unit.
 15. The airconditioner according to claim 14, wherein the control unit of theindoor unit decreases the opening degree of the indoor expansion valveby raising the target superheat degree of the indoor unit.
 16. The airconditioner according to claim 10, further comprising: a pressure sensorinstalled at a refrigerant inlet side of the compressor to measure thepressure of the refrigerant; and a control unit of an indoor unit toreceive data regarding the pressure of the refrigerant from the pressuresensor, installed at the refrigerant inlet side of the compressor,during a heating operation, and to adjust the pressure of therefrigerant to be lower than a designated pressure by controlling atarget superheat degree of the refrigerant inhaled into the compressor,if the pressure of the refrigerant is higher than the designatedpressure.